The present invention relates to a process for upgrading heavy hydrocarbonaceous materials, and more particularly, a process for upgrading heavy crude oils generally characterized by high specific gravities, high pour points, high viscosities and high contents of sulfur, metals, water, salt and conradson carbon for making coke suitable for metallurgical purposes.
In the typical delayed coking process, residual oil is heated by exchanging heat with liquid products from the process and is fed into a fractionating tower wherein light end products produced in the process or present in the residual oil are separated by distillation. The residual oil is then pumped from the base of the fractionating tower through a tubular furnace under pressure where it is heated to the required temperature and discharged into the bottom of the coke drum. The first stages of thermal decomposition reduce this residual oil to volatile products and a very heavy tar or pitch which further decomposes to yield solid coke particles. The vapors formed during the decomposition produce pores and channels in the coke and pitch mass through which the incoming residual oil from the furnace must pass. The incoming oil and decomposition vapors serve to agitate and maintain the coke mass and residual oil mixture at relatively uniform temperature. This decomposition process is continued until the coke drum is filled with a mass of coke with a small amount of pitch. The vapors formed leave the top of the coke drum and are returned to the fractionating tower where they are fractionated into the desired petroleum cuts. After the coke drum is filled with a mixture of coke particles and some tar, residual vapors are removed, and the coke is removed from the drum by hydraulic or mechanical means. This green delayed petroleum coke has particular crystalline and chemical properties which make it especially suitable for making carbon anodes for the aluminum industry, but the green coke must be calcined or carbonized by further treatment to produce a finished calcined coke product.
Due to the characteristics of the heavy crude oils of the type set forth above they cannot be processed economically by conventional processing. In addition to their low quality these crude oils are extremely temperature sensitive and decompose at relatively low temperatures. The processing and treatment of these crude oils at conventional conditions and in typical refining processes results in higher operating costs and the production of products which are predominantly of little value.
Naturally, it is highly desirable to provide a process for upgrading heavy crude oils so as to allow for the economic production of valuable petroleum products. The process of the present invention should allow for the economic production of coke suitable for metallurgical purposes.
Accordingly, it is a principal object of the present invention to provide a process for upgrading heavy crude oils.
It is a particular object of the present invention to provide a process for upgrading heavy crude oils for use in the production of metallurgical coke.
It is a further object of the present invention to provide a process for upgrading heavy crude oils wherein a hydrocarbon diluent is employed to facilitate control of temperature and residence time thereby prohibiting premature decomposition.
It is a still further object of the present invention to provide a process for upgrading heavy crude oils wherein the crude oil is carefully fractionated to maximize liquid yields during the coking step.
Further objects and advantages of the present invention will appear hereinbelow.